The present invention relates to a printed circuit board and a manufacturing method thereof wherein conductive material such as eyelet is inserted to the through-holes and caulked in order to connect the material with the electric circuit pattern which is printed on one or both sides of the board.
In the conventional printed board, through-hole are provided with conductive materials on their inner surface which are connected to the conductive pattern so as to assure the electric connection of the electric elements on mounting the parts on the board.
For the method of forming a conductive material on the inner surface of the through-hole of the board, various methods are applicable for this purpose, such as a method of applying plating on the through hole, a method of filling a conductive paint like a silver paste in the through-hole, and a method of fitting an eyelet to the hole.
The methods as above-mentioned have both advantages and disadvantages. The method of applying plating has a high reliability of conduction. But it is very high in cost, because so many processes and long working time are involved. Besides, an expensive installation is required for purifying waste water having generated in the plating process.
The method of applying a conductive paint is more economical in cost than plating. In this case, however, the electric resistance value is generlly large besides that it produces air bubbles or cracks in the paint layer, and for this reason the reliability as to electric conduction is low. Also it accompanies deterioration of products due to the heating which was incurred during the process.
In the method of using an eyelet, electric conduction is unstable because, as shown in FIG. 2, the flanges 41 and 42 of an eyelet 4 merely overlap on the conductive pattern 2 and 2, making no metallic connection with the conductive patterns. To improve the electric conduction, an applied pressure in caulking has only to be raised so that the flange will penetrate into the conductive pattern to obtain much closer contact with the conductive pattern. This can not be done, however, because the printed circuit board is sure to be damaged, being vulnerable to a higher pressure. For this reason, the eyelet is rarely used these days, notwithstanding its excellent advantages of low price and fitness to mass production.